Planting date and fertilizer affect antioxidants in pumpkin fruit

• As the planting date was delayed, antioxidant activities of pumpkin fruits decreased.
• Phenol, flavonoid, anthocyanin and proanthocyanidin concentrations were highest in fruits that were sown in April.
• Lesser rainfall, higher temperature and sunshine hour favored the antioxidant profile of pumpkin fruits.
• 90–180 kg ha−1 NPK (15:15:15) rates could provide optimal antioxidant contents of pumpkin fruit.
• Above 180 kg ha−1 NPK (15:15:15) fertilizer rate, antioxidants in pumpkin fruit diminished.

The concentration of antioxidants in vegetables are dependent on factors including sowing date and level of fertilizer applied. A field experiment was conducted in 2007 and 2008, to study influences of sowing date and fertilizer rate on antioxidant activities and concentrations of antioxidant phenolic compounds in pumpkin (Cucurbita pepo L) fruit. Sowing dates were: 1 April (1), 15 April (2), 1 May (3) and 15 May (4) and fertilizer levels of 0, 90, 180 and 270 kg ha−1 comprised of NPK (15:15:15) were used. The yield of pumpkin fruit ranged between 10 and 50 tons ha−1 depending on agronomical inputs. Plants established on 1 April had the highest antioxidant activity (81%). Concentrations of total phenol, flavonoid, cyanidin and proanthocyanidin in fruit decreased as sowing date was delayed. The highest antioxidant activities was between 90 and 180 kg ha−1 of NPK Concentrations of total phenol, flavonoid, cyanidin and proanthocyanidin in fruit was reduced at fertilizer rates above 180 kg ha−1. Early sowing of pumpkin and rates of between 90 and 180 kg ha−1 NPK could provide optimal antioxidant contents of pumpkin fruit.